This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on patent application Ser. No. 2002-0024939 filed in KOREA on May 7, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having a deflection yoke which can decrease a leakage magnetic field.
2. Description of the Related Art
In general, a television set or other image display devices using a cathode ray tube include a deflection yoke for deflecting an electron beam generated from an electron gun.
Here, a black and white cathode ray tube needs one electron gun, but a color cathode ray tube includes three in-line electron guns aligned in a row on a horizontal surface in order to reproduce color images with the mixture of red R, green G and blue B.
The color cathode ray tube employs a self-converging deflection yoke using an irregular magnetic field so as to converge three electron beams R, G and B emitted from the in-line electron guns into one point of a phosphor screen.
Here, the three electron beams emitted from the electron guns are deflected in a horizontal or vertical direction by a pincushion type horizontal deflection magnetic field or a barrel type vertical deflection magnetic field of the deflection yoke.
The beams deflected by the deflection yoke can be landed on the phosphor screen through a shadow mask.
FIG. 1 is a structure view illustrating a general cathode ray tube. Referring to FIG. 1, the cathode ray tube includes a panel unit 1, a funnel unit 2 connected to the panel unit 1, and a neck side 3 incorporating with the funnel unit 2.
A phosphor screen 5 coated with three dot or stripe-shaped color phosphor layers emitting R, G and B lights is installed on the inner surface of a panel 4 of the panel unit 1. In addition, a shadow mask 6 which is a color sorting electrode having a plurality of pores or slits is aligned at the inside portion to face the phosphor screen 5. The shadow mask 6 is connected to a frame 7, elastically supported by an elastic member 8, and also supported by the panel 4 through a stud pin 9. An inner shield 10 is fixed to the frame 7 in order to intercept an external magnetic field of electron beams deflected by a deflection yoke 13 to prevent the path of the electron beams from being changed.
Electron guns 14 are built in the neck side 3 for receiving a voltage and emitting R, G and B electron beams. Preferably, the electron guns 14 are in-line type electron guns aligned in a row on the same plane in the color cathode ray tube, for emitting three electron beams. In addition, convergence purity correction magnets (CPM) for converging the electron beams 12 emitted from the electron guns 14 into one point are positioned at the front end of the electron guns 14.
The deflection yoke 13 for horizontally or vertically deflecting the electron beams from the electron guns 14 is disposed on the outer surface of the funnel unit 2 at the rear end of the funnel unit 2, namely the front end of the neck side 3.
As illustrated in FIG. 2, the deflection yoke 13 includes a round-shaped holder 35 for forming a first flange 25 and a second flange 27 comprising a screen side 21 and a neck side 23, fixing horizontal deflection coils 29a and 29b, a vertical deflection coil 31 and a ferrite core 33 to predetermined positions, and insulating the vertical deflection coil 31 and the horizontal deflection coils 29a and 29b, the horizontal deflection coils 29a and 29b wound between the first flange 25 and the second flange 27 at the inside portion of the holder 35, for deflecting the electron beams emitted from the electron guns in the horizontal direction, the vertical deflection coil 31 wound between the first flange 25 and the second flange 27 at the inside portion of the holder 35, for deflecting the electron beams in the vertical direction, and the conical ferrite core 33 for improving magnetic efficiency by decreasing loss of the horizontal/vertical deflection magnetic field generated by the horizontal deflection coils 29a and 29b and the vertical deflection coil 31.
In general, the deflection yoke 13 generates the leakage magnetic field in the screen side 21 and the neck side 23. The leakage of the magnetic field is harmful to humans.
In order to prevent leakage of the magnetic field, cancel coils 37a and 37b are installed at the upper and lower portions of the first flange 25 of the deflection yoke 13. Here, a fetch line 41 fetched from a terminal plate 39 is connected to the horizontal deflection coils 29a and 29b through the cancel coils 37a and 37b. 
As shown in FIG. 4, the upper horizontal deflection coil 29a is connected in series to the pair of cancel coils 37a and 37b, and the lower horizontal deflection coil 29b is connected in series to a resistor R and a condenser C, which are re-connected in parallel. A saw tooth wave horizontal deflection current is applied to both ends H+ and Hxe2x88x92, thereby generating the horizontal deflection magnetic field. Accordingly, the electron beams emitted from the electron gun are horizontally deflected due to the horizontal deflection magnetic field.
In general, the conventional deflection yoke applies a current having a frequency of at least 15.76 kHz to both ends H+ and Hxe2x88x92 of the horizontal deflection coils 29a and 29b, and deflects the electron beams of the funnel unit 2 in the horizontal direction by using the thusly-generated pincushion type horizontal deflection magnetic field. On the other hand, the deflection yoke applies a current having a frequency of about 60 Hz to the vertical deflection coil 31, and deflects the electron beams in the vertical direction by using the thusly-generated barrel type vertical deflection magnetic field.
In addition, the self-converging type deflection yoke has been developed to converge the three electron beams onto the screen by using an irregular magnetic field due to the horizontal deflection coils 29a and 29b and the vertical deflection coil 31, without requiring a special additional circuit or device.
That is, the self-converging type deflection yoke adjusts the wiring distribution of the vertical deflection coil 31 and the horizontal deflection coils 29a and 29b, generates the barrel or pincushion type magnetic field to each portion, (for example the screen side 21, intermediate side 22 and neck side 23) in order for the three electron beams to have deflection force that differs according to their positions, and converges the electron beams to the same point in spite of a different distance between a starting point and ending point (namely, phosphor screen), thereby precisely hitting the corresponding phosphors.
In the case that the horizontal deflection magnetic field and the vertical deflection magnetic field are generated by transmitting the current to the horizontal deflection coils 29a and 29b and the vertical deflection coil 31, the horizontal/vertical deflection magnetic fields generated due to the horizontal/vertical deflection coils, it is difficult to deflect the electron beams toward the whole surface of the panel. Therefore, the ferrite core 33 of high magnetic permeability is used to minimize loss on a feedback path of the magnetic fields, thereby increasing magnetic efficiency and magnetic force.
On the other hand, as described above, the screen side 21 and the neck side 23 of the deflection yoke unnecessarily generates the leakage magnetic field in addition to the main deflection magnetic field for deflecting the electron beams in the horizontal or vertical direction. The leakage magnetic field may be harmful to humans. Particularly, leakage magnetic fields having extremely low frequencies (ELF) ranging from 5 Hz to 2 kHz or a very low frequency (VLF) ranging from 2 to 400 kHz are considerably harmful to humans. Therefore, a means for solving this problem is necessary.
One of the areas of research called for decreasing a length of an electric field, wherein a diameter and a slope angle of an end to the screen side in the deflection yoke are increased to obtain a high deflection angle, to remarkably generate the leakage magnetic field.
Also, a method for using the cancel coils 37a and 37b positioned at the upper and lower portions of the first flange 25 of the holder 35 as the means for decreasing the leakage magnetic field, or a method for increasing an interval between the end of the ferrite core to the screen side and the end of the horizontal deflection coil to the screen side has been employed.
FIG. 2 is a view illustrating the method for decreasing the leakage magnetic field by using the cancel coils, and FIG. 3 is a schematic cross-sectional view illustrating the deflection yoke using the cancel coils. As depicted in FIG. 3, since an unnecessary leakage magnetic field 45 is generated in the screen side (s) and neck side (n) of the deflection yoke in addition to a main deflection magnetic field 43 for deflecting the electron beams in the horizontal or vertical direction, the pair of cancel coils 37a and 37b are disposed at the upper and lower portions of the first flange 25 of the holder 35, so that a cancel magnetic filed 47 generated from the cancel coils 37a and 37b can offset the leakage magnetic field 45. Referring to FIG. 4, the cancel coils 37a and 37b are wired in a horizontal deflection circuit. The leakage magnetic field 45 generated in the screen side (s) of the horizontal deflection coils 29a and 29b and the cancel magnetic field generated due to the cancel current flowing through the cancel coils 37a and 37b have opposite directions to offset the leakage magnetic field.
However, the conventional deflection yoke has the following disadvantages:
First, as shown in the wiring circuit of FIG. 4, an inductance value of the cancel coils 37a and 37b is added in series to an inductance value of the horizontal deflection coils 29a and 29b, and thus the inductance value of the horizontal deflection coils 29a and 29b must be decreased to maintain the identical inductance value. When the inductance value of the horizontal deflection coils 29a and 29b is decreased, horizontal deflection sensitivity is reduced. In addition, reduction of the horizontal deflection sensitivity results in reduction of screen size. In order to obtain a screen size identical to the size before reduction of the sensitivity, the horizontal deflection current transmitted to the horizontal deflection coils must be increased. However, increase of the horizontal deflection current deteriorates a heat generation property of the deflection yoke, thus reducing the quality of the deflection yoke.
Secondly, when the cancel coils are used to decrease the leakage magnetic field, the cancel coils generate ringing 49 on a screen 48 as shown in FIG. 5. That is, the charged current is discharged due to stray capacitance between the coils wound around the pair of cancel coils 37a and 37b in a feedback time of the horizontal deflection current, thereby generating the ringing 49 at the left side of the screen 48. In order to remove the ringing, the resistor R and the condenser C are connected to the horizontal deflection coils 29a and 29b as shown in FIG. 4. However, the aforementioned method increases the price of the deflection yoke and complicates the operation for installing the components such as the resistor and the condenser on a printed circuit board.
Third, when the fetch line 41 of the cancel coils 37a and 37b is connected to the horizontal deflection coils 29a and 29b, the fetch line 41 comes off. Accordingly, an insulating tube must be provided to prevent sparks between the fetch line 41 and the horizontal deflection coils 29a and 29b, and a terminal for connecting an additional fetch line must be inserted into the terminal plate 39 for connection to the horizontal deflection coils 29a and 29b. As a result, the number of the required operations is increased to thereby reduce efficiency and productivity.
Fourth, the cancel coils 37a and 37b must be prepared and installed. That is, the cancel coils 37a and 37b are wound and installed by using a bobbin formed with an injection material. Thus, the injection type cancel coil bobbin must be individually produced. Since the cancel coil bobbin is individually produced, a mold needs to be produced (thus incurring additional expenses). In addition, specifications of the cancel coils are changed according to improvements of an image display device or variations of a model, and thus the cancel coil bobbin must be produced, wound and installed by using a new mold.
On the other hand, when the method for increasing the interval between the end of the ferrite core to the screen side and the end of the horizontal deflection coil to the screen side is used to reduce the leakage magnetic field, the application range of the interval is extremely narrow. Moreover, a high deflection angle greater than 100xc2x0 remarkably increases the leakage magnetic field. Therefore, the interval is not sufficient to offset the leakage magnetic field.
Recently, research for embodying a cathode ray tube with a reduced electric field have been actively conducted. It has been considered that, to reduce the electric field of the cathode ray tube, the deflection yoke is required to have a high deflection angle (greater than 110xc2x0 in monitor). However, the increased deflection angle reduces the deflection sensitivity of the deflection yoke, and remarkably increases the leakage magnetic field of the horizontal deflection coils. To solve the foregoing problem, a rectangular cone (RAC) deflection yoke has been suggested. The RAC deflection yoke obtains the stable deflection sensitivity at the high deflection angle, but fails to improve the leakage magnetic field property as follows:
The horizontal deflection magnetic field generated in the horizontal deflection coil consists of combinations of the magnetic field generated in the horizontal deflection coil itself and the magnetic field generated due to magnetization of the ferrite core by the magnetic field generated by the horizontal deflection coil. Particularly, the magnetic field generated by the ferrite core is incident on the inner surface of the ferrite core, transferred through a body of the ferrite core, and discharged vertically to the inner surface of the ferrite core. Accordingly, the leakage magnetic field generated through the screen side of the horizontal deflection coil is increased or decreased sensitively to the slope angle or diameter of the inner surface of the ferrite core. However, when the deflection angle of the deflection yoke is increased to obtain a high deflection angle, the diameter of the inner surface of the ferrite core for the deflection yoke is remarkably increased to generate the leakage magnetic field. Therefore, it is very difficult to decrease the leakage magnetic field at the high deflection angle.
In general, in order to measure the leakage magnetic field, a measuring device is installed separately from the panel of the cathode ray tube by 500 mm. According to the international specifications, when the current having a frequency of 15.75 kHz is transmitted, the leakage magnetic field is generally generated below 25 nT.
However, the distance between the deflection yoke and the measuring device is decreased due to reduction of the electric field. The leakage magnetic field is inversely proportional to the distance, and thus considerably increased. For example, in the case of the deflection yoke having a deflection angle greater than 110xc2x0, the leakage magnetic field ranges from 80 to 100 nT.
As described above, it is very difficult to reduce the leakage magnetic field both in the general deflection yoke and the deflection yoke for obtaining the high deflection angle.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Accordingly, one object of the present invention is to provide a cathode ray tube having a deflection yoke which can efficiently decrease a leakage magnetic field without using special auxiliary means, for example cancel coils.
It is another object of the present invention to provide a cathode ray tube having a deflection yoke which can overcome reduction of horizontal deflection sensitivity and deterioration of a heat generation property of the deflection yoke due to cancel coils.
It is yet another object of the present invention to provide a cathode ray tube having a deflection yoke which can decrease a leakage magnetic field generated by a ferrite core at a high deflection angle.
These and other objects and advantages of the invention are achieved by providing a cathode ray tube wherein, in a deflection yoke, a diameter of an end of a ferrite core to a screen side is 50% to 85% of a diameter of an end of a horizontal deflection coil to a screen side, and an interval between the end of the horizontal deflection coil to the screen side and the end of the ferrite core to the screen side is 27% to 505 of a length of the horizontal deflection coil in a tube axis direction. The cathode ray tube has a deflection angle greater than 110xc2x0.
According to another aspect of the invention, there is provided a TPS type cathode ray tube wherein, in a deflection yoke, a diameter of an end of a ferrite core to a screen side is 50% to 85% of a diameter of an end of a line deflection coil to the screen side, and an interval between the end of the line deflection coil to the screen side and the end of the ferrite core to the screen side is 27% to 50% of a length of the line deflection coil in a tube axis direction.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.